Laterite nickel and cobalt ore deposits generally contain oxidic type ores, limonites, and silicate type ores, saprolites, as two layers in the same deposits, separated by a transition zone. To minimise the equipment size for processing either the saprolites or the limonites by commercial processes, high grade limonite and saprolite are preferred. This leads to the lower grade ores and transition ores in some deposits being rejected as waste.
The higher nickel content saprolites tend to be treated by a pyrometallurgical process involving roasting and electrical smelting techniques to produce ferronickel. The power requirements and high iron to nickel ore ratio for the lower nickel content limonite, saprolite, and limonite/saprolite blends in the transition zone make this processing route too expensive for these ores.
The high nickel and cobalt content limonite is normally commercially treated hydrometallurgicaly by a high pressure acid leach process, or by a combination of pyrometallurgical and hydrometallurgical processes, such as the Caron reduction roast-ammonium carbonate leach process.
The above processes generally require “whole ore” processing as there is no effective method to beneficiate the ore. This has the disadvantage that the mineralogical fractions of the ore which may contain lower metal values effectively dilute the total treated ore quality and increase recovery costs.
The conventional treatment of saprolite to produce ferronickel, involves a drying step, followed by a reduction roast step to partially convert the nickel oxides to nickel, and smelting in an electrical furnace. This is a highly energy intensive process as the ratio of total ore to nickel is typically forty to one, and most of the power is expended in melting slag. It requires a high grade saprolite source to make it economic. It also has the disadvantage that financial value of any cobalt in the ore, which reports to the ferronickel, is not realised.
An improvement to this process would be to produce ferronickel directly from a nickel intermediate, eliminating the energy requirement to melt more than 95% of the ore.
It is a desired feature of the present invention to provide a simpler, less energy intensive, and lower capital investment process which overcomes or at least alleviates one or more of the difficulties associated with the prior art.
Nickel hydroxide is produced as an intermediate nickel compound commercially in the Cawse Plant in Australia. In the Cawse process, lateritic nickel ore is subjected to a high pressure sulfuric acid leach to extract the nickel and cobalt, along with other impurities. Waste ore and some impurities are separated from the leachate after partial neutralisation, and a mixed nickel cobalt hydroxide precipitated by further neutralisation with magnesium oxide.
Nickel hydroxide intermediate production by a similar process is also described in the prior art. For example, it may be produced as an intermediate from the leachate from high or atmospheric pressure acid laterite leaching or a combination of both, heap leaching of laterite or nickel sulfide ores or concentrates, or high pressure or atmospheric pressure leaching of sulfide ores or concentrates. The literature also teaches that nickel hydroxide may be produced from acidic nickel sulfate solutions produced as eluates, strip solutions, or raffinates from solvent extraction or ion exchange treatment of the prior mentioned process leachates or leach slurries.
International application PCT/AU2005/001360 in the name of BHP Billiton SSM Technology Pty Ltd discloses a process for the production of ferronickel or nickel matte by combined hydrometallurgical and pyrometallurgical processes. In the process disclosed in this specification, the nickel and iron are selectively absorbed on to a resin in an ion exchange process, eluted from the resin with sulfuric acid and the eluate is neutralised to precipitate a mixed nickel iron hydroxide product. The mixed nickel iron hydroxide product is then reduced directly to produce a ferronickel or nickel matte product.
The above discussion of documents, articles and the like is included in the specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these matters formed part of the prior art base or were common general knowledge in the field relevant to the present invention before the priority date.